This invention relates to a method for in-situ removal of hydrocarbon contaminants from groundwater. More particularly, this invention relates to a method for in-situ removal of hydrocarbon contaminants in aqueous solution from groundwater in which the groundwater containing the hydrocarbon contaminants is contacted with a permeable barrier comprising a peat material. The permeable barrier captures the hydrocarbon contaminants contained in solution within the groundwater, and the purified groundwater thereafter exits from the permeable barrier.
Loss of gasoline and other petroleum-derived hydrocarbons from underground storage tanks, pipelines and other facilities is one of the major sources of groundwater contamination in the United States. There are currently about 1.4 million underground tanks storing gasoline in the United States. It has been estimated that 10 percent or more of these tanks may be leaking and contaminating groundwater supplies.
Conventional technology for managing groundwater which has become contaminated with hydrocarbon contaminants such as petroleum products may be categorized into four categories: (1) containment of the contaminants using either physical barriers (i.e. slurry cutoff walls or sheet pilings) or hydraulic barriers created by a system of injection and pumping wells; (2) pumping of the contaminated groundwater to a treatment process at the surface, followed by disposal or reuse of the treated water; (3) removal of contaminated soil, with subsequent soil treatment or disposal; and (4) in-place stabilization of aquifer contaminants. Frequently, in practice, a combination of one or more of these alternatives is used, e.g. excavation of the most highly contaminated soil combined with a pump-and-treat process for contaminated groundwater.
Although conventional groundwater restoration techniques are effective when properly designed and implemented, they continue to have numerous problems associated with them. These include: (1) large amounts of water to be treated; (2) undesirable by-products; (3) large and long-term disruption of the site; and (4) extensive amounts of time required for complete site restoration.
In view of the foregoing, it would clearly be advantageous to employ a method of removing hydrocarbon contaminants from groundwater in-situ, thereby treating the groundwater and simultaneously avoiding many of the problems attendant to the above-described methods. One in-situ technique for removing hydrocarbon contaminants from groundwater which has been suggested is the use of a permeable barrier in-situ which allows passage of groundwater therethrough but intercepts soluble contaminants, as disclosed, for example in B. M. Thomson & S. P. Shelton, "Permeable Barriers: A New Alternative for Treatment of Contaminated Groundwaters", in Proceedings of the Focus Conference on Southwest Groundwater Issues, Association of Groundwater Scientists and Engineers, pp. 441-53 (Albuquerque, N.M. 1988). However, the makeup of such a permeable barrier is critical in the in-situ removal of hydrocarbon contaminants from groundwater, in that the material employed must be relatively low in cost, compatible with the surrounding soil and topology, yet capable of removing the undesired contaminants from groundwater.
Peat has long been valued for many uses, particularly as a fuel, in agricultural and horticultural uses, and as a raw feed stock for a variety of chemicals. More recently, the use of peat materials in environmental pollution control applications has been studied, as described, for example, in J. K. McLellan & C. A. Rock, "The Application of Peat in Environmental Pollution Control: A Review", in International Peat Journal, vol. 1, pp. 1-14 (1986). More particularly, the use of peat and peat mixtures as an absorbent for the removal of surface oil on the surface of the ground or water, typically caused by an oil spill, has been previously disclosed. For example: U.S. Pat. No. 4,778,602 (Allen) discloses the use of a chemically modified peat material as a filtering medium and for the removal of oil from water surfaces by sprinkling the finely powdered filtering media on the oil-laden water surface; European Patent Application No. 075,384 discloses a process for preparing an oil absorbent peat material which comprises mixing peat with an alkaline earth metal basic product, drying the mixture, adding additional alkaline earth metal basic product to the mixture, and heating the mixture until the peat has the desired moisture content; and Canadian Patent No. 1,135,241 (Mackey) discloses a method for collecting oil from oil spills by applying diatomaceous earth and a buoyant material which may be peat to an oil spill on a water surface, the buoyant material acting to cause the clay-like product created by the oil-soaked diatomaceous earth to float for eventual removal.
However, leaking underground gasoline storage tanks, pipelines and the like typically cause contamination of a given groundwater stream by a mechanism wherein the individual organic contaminants contained therein are in solution with the aqueous groundwater stream. Thus, the requirements for removal of hydrocarbon contaminants such as gasoline and its components (e.g. benzene, toluene, and xylene) in solution from groundwater are distinct from those where hydrocarbons such as oil are removed by absorption from ground or water surfaces; i.e., the removal of hydrocarbon contaminants in aqueous solution from groundwater requires adsorption of the contaminants by an adsorbing medium capable of removing the contaminants in aqueous solution from the groundwater.
It is one object of this invention to provide a method for in-situ removal of hydrocarbon contaminants such as gasoline and its components from groundwater, in which groundwater containing hydrocarbon contaminants in aqueous solution is contacted in-situ with a permeable barrier comprising a peat material. It is one feature of this invention that the removal of hydrocarbon contaminants from aqueous solution with the groundwater is accomplished with greater efficiency, lower capital costs, lower operating costs, and reduced surface and other environmental disturbances in comparison with typical conventional techniques as previously described. Thus, the method of this invention advantageously has lower costs associated with it than conventional means of removing hydrocarbon contaminants in aqueous solution from groundwater, and in addition advantageously avoids large disruptions of ground surfaces, as well as the use of large quantities of water, which often are difficult to obtain, and may themselves become contaminated, posing further problems of treatment and disposal.
It is another object of this invention to provide a method for in-situ removal of hydrocarbon contaminants such as gasoline and its components from groundwater, in which hydrocarbon contaminants in aqueous solution are removed by contacting the groundwater in-situ with a permeable barrier comprising in series a combination of an immobilized nutrient layer and a peat material layer, with the permeable barrier positioned substantially perpendicular to the groundwater stream incident thereto. It is another feature of this invention that the immobilized nutrient layer enhances the natural degradation of the hydrocarbon contaminants, and any contaminants which are not degraded in the immobilized nutrient layer are adsorbed by the peat material layer, thus advantageously avoiding large disruptions of ground surfaces and the use of large quantities of water.
It is yet another object of this invention to provide a method for in-situ removal of hydrocarbon contaminants in solution in groundwater in which the groundwater is contacted in-situ with a permeable barrier comprising a peat material, wherein the peat material is characterized by having ash content, birefringent organic content, fiber content, guaiacyl lignin pyrolysis product content and furan pyrolysis product content values within a specified range, and thus is more effective in removing hydrocarbon contaminants in solution with groundwater than other peat materials not characterized by having such values. It is yet another feature of this invention that a peat material characterized by having such values of the above-described parameters, as specified herein, advantageously adsorbs hydrocarbon contaminants such as gasoline and its components in aqueous solution in groundwater.
It is yet another object of this invention to provide a method for in-situ removal of hydrocarbon contaminants in solution in groundwater, in accordance with this invention, wherein naturally occurring peat materials are employed in the permeable barrier having the contaminant-laden groundwater stream incident thereto. It is yet another feature of this invention that naturally occurring peat materials may be employed in the permeable barrier of this invention, thus advantageously avoiding the use of chemically treated peat materials, which are typically more expensive and less readily available than naturally occurring peat materials, and which may have other attendant problems associated with their use in-situ.